The present invention is related generally to electronic sensors for detecting airborne chemical and biological agents. More specifically, the present invention is related to microelectromechanical systems (MEMS) which can detect harmful chemical and biological agents.
Air or gas phase sensing and measurement systems are currently used in many applications, such as industrial process controls, environmental compliance measuring, and explosive detection. In one example, on-line gas chromatography and on-line optical spectroscopy are used to measure process conditions using the gas phase components. In another example, the concentration of combustion gases and stack particulates are measured to insure environmental regulatory compliance. Such systems often transport the gas to be measured to the sensor or sensors for property measurements using a pump. The pumps used to drive the gas are often bulky and consume large amounts of power. This often limits the application of such systems. In addition, many such sensor systems have a single pump for driving the gas to the sensors. As such, the failure of the pump may cause the entire system to fail.
The present invention provides an integrated pump and sensor for improved detection and reliability. Preferable, many micro-pumps are provided wherein each micro-pump is in fluid communication with one or more miniature sensors. More preferably, the micro-pumps are mesopumps formed using MEMS technology, wherein each sensor has a dedicated and often individually controllable pump. Such pump/sensor systems can be easily mass produced into a 3D array of integrated lightweight pump-sensors systems. Such system can be used in many applications, including medical gas phase diagnosis, industrial control sensing, agriculture measurements, landmine detection, harmful chemical and biological agent detection, etc.
An illustrative embodiment of the present invention provides an integrated mesopump-sensor assembly suitable for disposition within two- and three-dimensional arrays having small dimensions. One mesopump is formed of an electrostatically attractable flexible diaphragm disposed through cavities or pumping chambers formed between two opposing electrostatically chargeable layers.
The mesopump may be formed of a first, upper layer of a dielectric material having a concave cavity formed in the material lower surface, the cavity having a conductive layer covered by an insulating dielectric layer. A second, lower layer of similar construction may be disposed beneath the first layer in an opposing orientation such that the two concave cavities form a pumping chamber. An interposing layer of a flexible electrically conductive diaphragm material is provided between the upper and lower layers. The diaphragm could be made of insulating material covered on both sides with conductive layers. The flexible diaphragm is attracted toward either the upper or lower layer by applying an electrical potential to either the upper or lower layer conductive portion relative to the interposing diaphragm layer.
Another (second) layer of pumping chambers may be formed by forming concave cavities in the lower surface of the second layer, followed by a second diaphragm layer, followed by an opposing third layer having opposing concave cavities to form a second level of pumping chambers, as further described below. During operation, fluid to be sensed is passed from a first pumping chamber downward to a second chamber, laterally to a third chamber, upward to a fourth chamber, and out through an outlet conduit.
One group of sensors includes chemo-resistive sensors that vary in electrical resistance and/or impedance in response to the presence of an analyte. Various chemo-resistive sensors may vary in composition such that the sensor outputs vary in response to the presence of an analyte from sensor to sensor. The outputs of such single sensors may be unable to identify a particular analyte, but can be collectively analyzed according to Principle Component Analysis (PCA) techniques to identify particular compounds. The multiplicity of sensors that can be provided by two- and three-dimensional arrays of mesopump sensors are well suited to the multiple inputs used by PCA.
Another type of suitable sensor utilizes chemo-fluorescent compounds which fluoresce in response to the presence of general or particular compounds. Many other sensor types are suitable for use with the present invention, including spectroscopic sensors over either broad or narrow wavelengths.
The mesopump-sensors can be arrayed into stacks and coupled to controllers, including micro-controllers or general purpose computers. Computer programs or logic within the controllers can be used to sequence the operation of the pumping chambers and to analyze the sensor outputs. One embodiment includes controller programs that perform PCA. Controller programs can be utilized to operate pump sequencing in either bi-directional or uni-directional modes, depending on the limitations of the mesopumps and on the intended application. Bi-directional modes of operation can be used to push and pull fluid to be sampled past the sensor and can also be used to economize on the number of chambers needed to form a pump channel.
In one mode of operation, a bi-directional xe2x80x9cshallow breathingxe2x80x9d mode is utilized to draw a fluid such as air into the mesopump-sensor just past the sensor, then expel the fluid so as to minimize any fouling of the mesopump interior past the sensor. Bi-directional modes of operation can also be used to attempt to clean filters of particles and to push clean, purged air past a sensor, where the sensor may have become saturated. Filters may be provided on one or all external fluid orifices, and may include an impactor type filter to trap particles that have entered the mesopump.
The integrated mesopump sensors can provide a large number of small, lightweight, and closely spaced sensors that can be used advantageously to detect airborne agents, including harmful chemical and biological agents or trace amounts of TNT or other explosives from buried land mines. The large numbers of individually controllable sensors also may provide a system that can sequentially operate sensors that are likely to become saturated or poisoned, and to activate pumping and detailed sensing only in response to general sensor outputs or triggers.